Kenaf-fiber-reinforced resin composition

ABSTRACT

An object of the present invention is to provide a fiber-reinforced resin composition suitable for producing molded articles for products such as electrical and electronic equipment. The object has been achieved by a biodegradable resin composition containing a kenaf fiber, which contains a kenaf fiber in an amount of 10 to 50% by mass. In this case, the biodegradable resin is preferably a crystalline thermoplastic resin, particularly polylactic acid. The average fiber length (number average fiber length of the fibers excluding fragments) of the kenaf fiber is preferably 100 μm to 20 mm, and the kenaf fiber preferably contains a kenaf fiber having a fiber length of 300 μm to 20 mm. As the kenaf fiber, a fiber prepared from bast of kenaf is preferred.

This application is a National Stage application of PCT/JP2004/000100,filed Jan. 9, 2004, which claims priority from Japanese patentapplication JP 2003-003856, filed Jan. 10, 2003, and Japanese patentapplication JP 2003-407799, filed Dec. 5, 2003. The entire contents ofeach of the aforementioned applications are incorporated herein byreference.

1. Technical Field

The present invention relates to a fiber-reinforced resin compositionused for products such as electrical and electronic equipment. Morespecifically, the present invention relates to a resin composition formolding containing kenaf fibers in a biodegradable resin, which isexcellent in the balance of properties such as heat resistance andrigidity, cost-friendly, excellent in environmental compatibility andsuitable for use for electrical and electronic equipment.

2. Background Art

Recently, along with thin-modeling and downsizing of electrical andelectronic equipment products, there is an increasing demand forfiber-reinforced resin compositions for molding such products. Commonfiber-reinforced resin compositions use glass fiber or carbon fiber as areinforcing fiber. These fibers are effective for improving heatresistance and strength, but on the other hand, plant materials are nowattracting attention as a reinforcing material from an environmentalviewpoint.

As such plant materials, a technique involving mixing pulp, plant fiberor crushed materials of plants such as kenaf with a thermoplastic resinor a thermosetting resin is disclosed. For example, regarding athermoplastic resin, as Patent Documents 1 to 6 and non-Patent Document1 describe, a composition of a fiber originated from a plant or crushedmaterials of a plant and a thermoplastic resin is disclosed.

Patent Document 1 describes that a resin composition containing kenafstem fragments, composed of 80 to 50% by mass (% by weight) of kenafstem fragments broken or cut with maintaining the original structure and20 to 50% by mass (% by weight) of a synthetic resin can provide amolded article which is free from mill ends, lightweight and has highrigidity and a high aspect ratio.

Kenaf is an annual plant belonging to the mallow family classified intothe same category as hibiscus, and it grows rapidly, reaching as high as4 to 5 m and as wide a stem diameter as 4 to 5 cm, and in the fastestcases, its growth is about 10 cm per day. In this way, kenaf has a fastphotosynthetic rate and thus can absorb a large amount of carbondioxide, and it is therefore attracting attention as one of the means tosimultaneously solve the global problems of global warming caused bycarbon dioxide and deforestation. The stem of kenaf consists of bastwhich is a fiber of stem bark and xylem existing at the center of thestem, each of which has different features. The bast accounts for 30%(mass ratio) of the kenaf stem and has a feature that it is long andexcellent in strength similarly to fiber of coniferous trees. This bastfiber is used for ropes, cloths, bags and papers. The xylem comprises70% (mass ratio) of the kenaf stem and is used as reinforcing materialsof houses or materials of canoe, and has a feature that the fiber isshorter than the fiber of broad leaf trees. The whole stem composed ofbast and xylem resembles broad leaf tree fiber, which can be formed intopaper like high quality Japanese washi.

Non-Patent Document 1 describes that a composite material in which anon-woven fabric prepared from kenaf bast is combined with polylacticacid by a wet process has both high mechanical properties and heatresistance.

Patent Document 2 discloses a thermoplastic resin for a transferringmember which has improved mechanical strength and heat resistance byincorporating 30 to 55 parts by weight of pulp into a thermoplasticresin. Thermoplastic resins including polypropylene, polyethylene,polystyrene and ABS resin are studied.

Patent Document 3 describes a container for a photosensitive materialusing a thermoplastic resin composition containing not less than 50% bymass (% by weight) of pulp composed of natural fiber such as kenafhaving an average fiber length of 0.3 to 3.0 mm. It is disclosed thatthe container for a photosensitive material is excellent in dimensionalstability and disposal properties, free of odor and does not affect thephotographic performance. Thermoplastic resin including petroleum resin,more specifically polyolefin resin, is studied. It is described that ina composition in which only plant fiber is mixed with polyolefin resin,it is difficult to disperse the plant fiber uniformly, and whileuniformity can be improved by reducing the mixing ratio of the plantfiber, physical properties such as rigidity, dimensional stability, heatresistance and coating property are decreased; and to increase themixing ratio of plant fiber for achieving such physical properties andto improve dispersibility, combination of rosin or an analogue thereofand a plasticizer is extremely important.

Patent Document 4 describes a biodegradable resin composition containing1 to 30 parts by weight of plant fiber powder crushed to a fiber lengthof 200 μm or less, 99 to 70 parts by weight of aliphatic polyester resinsuch as polylactic acid and an alkaline earth metal oxide. It isdescribed that in the case of this resin composition, by blendinginexpensive plant fiber, the cost of the composition can be reduced andthe biodegradation rate of the plant fiber composition can be increased.The publication describes that when the amount blended of plant fiber is1% by mass or less, the effect of the invention cannot be obtained andwhen the amount is 30% by mass or more, the fluidity of the compositionis decreased and the molding processability is poor.

Patent Document 5 describes a method of effective use of plant fiberwhich has been conventionally discarded, by using a resin compositioncontaining 40 to 60% by mass (% by weight) of fiber of plant such asstraw, crushed to 60 to 100 mesh (150 μm to 250 μm) and 60 to 40% bymass (% by weight) of polylactic acid.

Patent Document 6 describes a composite material containing 1 to 100parts by mass of cellulose fiber composed of hard linen fiber having afiber length of 3 to 10 mm and 100 parts by mass of a biodegradableresin such as polylactic acid, which has an improved mechanical strengthwithout decrease in biodegradability.

[Patent Document 1] Japanese Patent No. 3316211 (paragraph 0004)

[Patent Document 2] Japanese Patent Laid-Open No. 6-239516 (paragraph0007)

[Patent Document 3] Japanese Patent Laid-Open No. 2000-219812 (paragraph0013 to 0020)

[Patent Document 4] Japanese Patent Laid-Open No. 10-273582 (paragraph0005, 0006, 0011)

[Patent Document 5] Japanese Patent Laid-Open No. 2002-69303 (paragraph0013, 0014)

[Patent Document 6] Japanese Patent Laid-Open No. 2001-335710 (paragraph0003, 0004)

[Non-Patent Document 1] Takashi Nishino, “New Technology for FormingCellulose Composite”, CONVERTECH p 36-39, August, 2002.

PROBLEMS TO BE SOLVED BY THE INVENTION

Outer housing materials of electrical and electronic equipment arerequired to fulfill, in addition to physical properties for a merepackage such as strength, manufacturing requirements such as moldabilityand design requirements such as good appearance (color shade andtexture). The manufacturing requirements include, for example,applicability of injection molding which is a universal technique forproducing outer housing materials of electrical and electronicequipment, which means that raw materials (a mixture of resin and fiberin the case of fiber-reinforced resin) are to be flowable at moldingtemperatures and the fiber can be uniformly dispersed in the resin, andthat the problems such as clogging of composition in a molding machineare not caused.

However, it was difficult to apply conventional resin compositionsreinforced by pulp, plant fiber or crushed materials of plant toelectrical and electronic equipment. For example, in the compositiondescribed in Patent Document 1, the fiber length of the kenaf stemfragments used is as long as 20 to 100 mm and the mixing ratio of kenafis as high as 50 to 80% by mass, and therefore although the compositionis excellent in strength, it has a problem that application to outerhousing materials of electrical and electronic equipment, in particularelectronic equipment, where molding with fine irregularities and moldingin a thickness of 5 mm or less are required is difficult. Currently,mobile electronic devices require a thickness of 2 mm or less, and thelength of the fiber that can be used is even more limited. Further, themethod of preparing a composite material by impregnating polylactic acidinto kenaf non-woven fabric described in non-Patent Document 1 involvesa problem that it is difficult to apply the method to outer housingmaterials of electrical and electronic equipment products as far asmoldability is concerned.

In addition, the present inventors have studied application of thecomposition described in Patent Document 2 to an outer housing materialof electrical and electronic equipment, and have found that althoughthere was no problem for injection molding, heat resistance wasinsufficient under load of 1.80 MPa and the reinforcing effect by pulpwas not adequate.

The present invention has been made in order to solve theabove-described problems and aims at providing a biodegradable plantfiber-reinforced resin composition that can be used for an outer housingmaterial of electrical and electronic equipment products. Morespecifically, it aims at providing a resin composition which can bemolded by injection molding generally used for producing outer housingmaterials of electrical and electronic equipment products.

DISCLOSURE OF THE INVENTION

To solve the above-described problems, the present inventors havestudied various possible plant fibers and from the strength of fiber,compatibility with biodegradable resin and superiority in approaches toglobal environmental problems, fiber obtained from kenaf has beenselected. Then, the content in resin and the properties of the fiberhave been studied in detail, and they have completed the followinginvention.

The kenaf fiber-reinforced resin composition of the present invention ischaracterized in that the composition is a biodegradable resincomposition containing a kenaf fiber, and contains the kenaf fiber in anamount of 10 to 50% by mass. The content of the kenaf fiber is morepreferably 15 to 40% by mass.

According to this invention, as the content of the kenaf fiber is set tothe above-mentioned range, precise injection molding needed formanufacturing molded articles such as electrical and electronicequipment products is applicable, and an effect can be obtained that themechanical strength is improved and the heat resistance is alsoimproved. In this regard, moldability by injection molding means thatraw materials (a mixture of resin and fiber in the case offiber-reinforced resin) are flowable at molding temperatures, the fibercan be uniformly dispersed in the resin, and that problems such asclogging of composition in a molding machine do not occur.

In the kenaf fiber-reinforced resin composition of the presentinvention, the biodegradable resin is preferably a crystallinethermoplastic resin, particularly preferably polylactic acid.

Further, in the kenaf fiber-reinforced resin composition of the presentinvention, the average fiber length of the kenaf fiber (number averagefiber length of the fibers excluding fragments) is preferably 100 μm to20 mm, and the kenaf fiber preferably contains a kenaf fiber having afiber length of 300 μm to 20 mm.

The kenaf fiber is preferably prepared from bast of kenaf.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a micrograph of bast fiber (kenaf fiber prepared only frombast) used in Example of the present invention;

FIG. 2 is a micrograph of bast fiber (kenaf fiber prepared only frombast) used in Example of the present invention; and

FIG. 3 is a micrograph of whole stem fiber (kenaf fiber prepared fromwhole stem combining bast and xylem) used in Example of the presentinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

First, the kenaf fiber constituting the kenaf fiber-reinforced resincomposition of the present invention is described in detail.

The kenaf fiber constituting the kenaf fiber-reinforced resincomposition of the present invention is obtained by breaking, cutting orcrushing kenaf. In the present invention, the kenaf fiber is a genericterm referring to fiber prepared from xylem, bast or whole stemcombining xylem and bast of kenaf, and blended fiber thereof. In thefollowing description, fiber prepared from xylem is referred to asligneous fiber, fiber prepared from bast is referred to as bast fiber,and fiber prepared from whole stem is referred to as whole stem fiber.In the present invention, any kenaf fiber can be used, but bast fiber,whole stem fiber, or a blend of ligneous fiber and bast fiber or wholestem fiber is preferably used. Using bast fiber alone is particularlypreferred. Bast fiber has high reinforcing effect and by using bastfiber alone, the effect of reinforcing biodegradable resin which forms amolded article can be further improved.

The kenaf fiber employed in the present invention preferably has anaverage fiber length of 100 μm to 20 mm, and contains at least a kenaffiber having a fiber length of 300 μm to 20 mm. Since the resincomposition of the present invention contains a kenaf fiber of suchranges, the effect of reinforcing biodegradable resin which forms amolded article can be further improved. The average fiber length of thekenaf fiber is more preferably 1 to 10 mm, whereby the effect ofreinforcing biodegradable resin can be further increased. Here, theaverage fiber length means a number average fiber length of the fibersexcluding fragments, and fragments are defined as those less than 50 μmin the length in the longitudinal direction.

When the kenaf fiber contained has an average fiber length of more than20 mm, or kenaf fiber having a fiber length of more than 20 mm isincluded, the fiber tends not to be uniformly dispersed in the resin ina manufacturing machine such as a kneader when producing kenaffiber-reinforced resin composition. When a fiber having a length muchgreater than the thickness of a molded article is included, appearanceand touch of the molded article are deteriorated, and the maximum fiberlength is therefore desirably not more than 10 times, more desirably notmore than 5 times the thickness of the molded article. In addition, inthe case of injection molding, clogging of resin composition in amolding machine may be caused. In particular, it is desired that kenaffiber having a fiber length of more than 50 mm is removed before beingintroduced into the kneader. On the other hand, when using a kenaffiber-reinforced resin composition containing only a kenaf fiber havinga fiber length of less than 300 μm as a kenaf fiber, the reinforcingeffect according to the kenaf fiber is not sufficient.

Studies by the inventors revealed that when kenaf fibers having anaverage fiber length of 100 μm to 20 mm and including at least kenaffibers having a fiber length of 300 μm to 20 mm are incorporated into acrystalline thermoplastic resin such as aliphatic polyester resin likepolylactic acid, not only the strength is improved, but also the heatresistance indicated by heat distortion temperatures is improved.Although the mechanism is not clear, it is assumed as follows: in thematerial resin, crystalline portions and amorphous portions are mixed,and as the amorphous portions are fluidized at lower temperatures, thekenaf fiber incorporated into the amorphous portions prevent theamorphous portions from being fluidized, and as a result, the heatresistance is improved. This heat resistance improving effect is furtherincreased when kenaf fibers having an average fiber length of 1 to 10 mmare used as in the above reinforcing effect.

The impact strength of the kenaf fiber-reinforced resin composition willnow be described in detail.

To improve the impact strength of the kenaf fiber-reinforced resincomposition, kenaf from which fragments are removed is preferably used.Because of inadequacy in adhesion between the kenaf fiber and the resin,the energy at impact is assumed to be absorbed into the friction energyneeded for detaching fiber. Therefore, by removing such fragments, thefriction energy needed for detaching fiber at impact is increased andthe impact strength can be thus improved. Fragments in kenaf fiber canbe removed by a known method. Examples thereof include a method using acentrifugal force such as a cyclone separator (Japanese PatentApplication No. 7-090180), a method using mechanical classification(Japanese Patent Application No. 2001-348794) and a method using a dustcollector. The average fiber length of the kenaf fiber from whichfragments are removed is preferably 100 μm to 20 mm, more preferably 1to 10 mm.

As a method of preparing a resin composition composed of kenaf fiberfrom which fragments are removed, kneading according to a methodinvolving a low shearing force such as using a single-screw extruder ispreferred. By lowering the shearing force, the fiber length of kenaf ismore easily maintained. Even in a twin-screw extruder, the shearingforce can be lowered by changing the configuration of the screw.

As another method of improving the impact strength, a flexibilizer maybe used. For such flexibilizer, known substances can be used andexamples thereof include the following.

Plasticizers such as polymer blocks (copolymers) selected from polyestersegments, polyether segments and polyhydroxy carboxylic acid segments,block copolymers in which a polylactic acid segment, an aromaticpolyester segment and a polyalkylene ether segment are mutuallycombined, block copolymers composed of a polylactic acid segment and apolycaprolactone segment, polymers containing unsaturated carboxylicacid alkyl ester unit as a main component, aliphatic polyesters such aspolybutylene succinate, polyethylene succinate, polycaprolactone,polyethylene adipate, polypropylene adipate, polybutylene adipate,polyhexene adipate and polybutylene succinate adipate, polyethyleneglycol and esters thereof, polyglycerol acetic acid ester, epoxidizedsoybean oil, epoxidized linseed oil, epoxidized linseed oil fatty acidbutyl, adipic acid aliphatic polyester, acetyl tributyl citrate, acetylricinolic esters, sucrose fatty acid ester, sorbitan fatty acid ester,adipic acid dialkyl ester and alkyl phthalyl alkylglycolate.

The flexibilizers described above can absorb the energy at impact.Generally, addition of a flexibilizer leads to decrease in heatresistance, but by using kenaf together, both the heat resistance andthe impact strength of the biodegradable resin can be improved.

As a method of improving impact strength, high strength fiber can beused. Examples of high strength impact resistant fiber include polyamidesuch as aramid and nylon, polyesters such as polyallylate andpolyethylene terephthalate, ultra-high strength polyethylene,polypropylene, teflon® fiber such as PTFE, carbon fiber and metal fiber.

Aramid fiber and polyarylate fiber, which are aromatic compounds, areparticularly desirable from the viewpoint that they have higher heatresistance and higher strength, and are paler than other fiber and thusdo not damage design properties when added to the resin and have lowspecific gravity.

As for the shape of the high strength impact resistant fiber, thosehaving a polygonal, amorphous or irregular fiber cross-section, notcircular, and having a high aspect ratio and a short fiber diameter havea greater contact area with resin, and therefore the effect of detachingfiber from matrix is increased and the effect of reducing impact bydetachment of fiber is also increased, whereby the impact strength isimproved. In addition, by using fiber which has irregularities formed onthe surface, fiber shaped like a wedge in which both ends of the fiberis broadened compared to the central part, fiber constricted in somepart or a non-linear, frizzled fiber, the friction when the fiber isdetached is increased to improve impact strength.

Further, the high strength fiber may be subjected to a surface treatmentwhere necessary in order to increase compatibility with the resin whichis the base material or to enhance entanglement between fibers. As suchsurface treatment, treatment by a silane or titanate coupling agent,ozone or plasma treatment, and in addition, treatment by an alkylphosphoric acid ester surfactant are effective.

However, the method is not limited to these, and methods generally usedfor surface modification of fillers may be used.

The moisture content of the kenaf fiber is not more than 4% by massbased on the mass of the kenaf fiber. When the moisture content of thekenaf fiber is more than 4% by mass, deterioration of appearance due to“mold cavity” or “blister” may be caused upon molding of the resincomposition. The moisture content of the kenaf fiber is particularlypreferably not more than 1% by mass based on the mass of the kenaffiber. When the moisture content of the kenaf fiber is not more than 1%by mass, not only the obtained molded article has excellent appearance,but also a stable reinforcing effect can be exerted on every part of themolded article.

Further, it is also preferable to remove volatile components other thanmoisture in advance, and this leads to exertion of stable reinforcingeffect. As for the volatile components other than moisture in the kenaffiber, the amount to be generated at 130° C. is particularly preferablynot more than 1% by mass based on the mass of the kenaf fiber, and thisleads to exertion of stable reinforcing effect. In the case thatmoisture and volatile components are removed before melt-kneading kenaffiber and resin or before introducing a kenaf fiber-reinforced resincomposition into a molding machine, the kenaf fiber is dried atpreferably 30 to 300° C., more preferably 80 to 150° C.

In the kenaf fiber-reinforced resin composition of the presentinvention, the content of the kenaf fiber is preferably 10 to 50% bymass. When the content of the kenaf fiber is more than 50% by mass, thefluidity of the resin composition is remarkably decreased and problemsmay arise such that a satisfactory product shape or product patterncannot be achieved in injection molding often employed as a method ofmanufacturing electrical and electronic equipment products. Inparticular, the composition cannot be applied to outer housing materialsof electronic equipment which requires molding with fine irregularitiesor molding in a thickness of 5 mm or less. On the other hand, when thecontent of the kenaf fiber is less than 10% by mass, the flexuralmodulus of the obtained molded article is suddenly decreased, and thereinforcing effect is significantly reduced. The content of the kenaffiber is preferably within the range of 15 to 40% by mass.

When the biodegradable resin in the kenaf fiber-reinforced resincomposition of the present invention is a crystalline thermoplasticresin, in addition to the improvement in the mechanical strength, theheat resistance indicated by the heat distortion temperature isimproved. Heat resistance is greatly improved where the content of thekenaf fiber is between 10% by mass and 15% by mass, and it hardlychanges even if the content is more than 20% by mass. When thisphenomenon is considered based on the above-described heat resistanceimprovement mechanism which the present inventors assumed, it can beexplained that the effect of preventing the amorphous portions fromfluidizing is exerted at a content of not less than 10% by mass andreaches a ceiling beyond 20% by mass.

Further, a kenaf fiber subjected to a surface treatment can also be usedwhere necessary. The purposes of surface treatment are to improve thecompatibility with biodegradable resin and to improve the flameretardancy of the kenaf fiber.

As a method of surface treatment for improving the compatibility(synonymous with improvement in adhesion) between the kenaf fiber andthe biodegradable resin, treatment by a silane or titanate couplingagent, ozone or plasma treatment, and in addition, treatment by alkylphosphoric acid ester surfactant are effective. However, the method isnot limited to these, and methods generally used for surfacemodification of plant fiber may be used. By subjecting kenaf fiber tosuch surface treatment, the compatibility between the kenaf fiber andbiodegradable resin can be improved, and thus the effect of reinforcingthe biodegradable resin which forms a molded article can be furtherimproved.

Further, as a surface treatment for improving flame retardancy of thekenaf fiber, general flame retardant treatments for wood or paper may beemployed. For example, such method includes immersing kenaf fiber in anaqueous solution of phosphate such as barium phosphate, ammoniumphosphate or ammonium polyphosphate to form a flame-retardant phosphatelayer on the surface of the fiber. In addition, there is a methodcomprising immersing kenaf fiber in an aqueous solution of metalalkoxide containing silicon or boron, an aqueous solution in which thoseelements or a metal compound such as a metal oxide thereof are dissolvedusing acid or base, silicic acid, boric acid or an aqueous solution of ametal salt thereof to form a flame-retardant metal oxide or other metalcompounds on the surface of the fiber. By subjecting the kenaf fiber tosuch surface treatment, the flame retardancy of the kenaf fiber can beimproved, and therefore even when the mold processing temperature formolding is increased, the effect of reinforcing biodegradable resinaccording to kenaf fiber can be maintained well.

By using kenaf fiber which has undergone such surface treatment, theimpact strength of the kenaf fiber-reinforced resin composition can alsobe improved. The impact strength is improved probably because as thecompatibility between the kenaf fiber and the resin is improved, theenergy needed for detaching fiber at impact is increased.

The biodegradable resin constituting the kenaf fiber-reinforced resincomposition of the present invention will now be described.

As a biodegradable resin material which is the raw material of thebiodegradable resin, biodegradable monomers obtained by being mainlyartificially synthesized, oligomers and polymers composed of aderivative of a biodegradable monomer obtained by being mainlyartificially synthesized, modified oligomers and modified polymerscomposed of a biodegradable monomer obtained by being mainly naturallysynthesized, oligomers and polymers composed of a derivative of abiodegradable monomer obtained by being mainly naturally synthesized,and modified oligomers and modified polymers may be used.

Examples of artificially synthesized biodegradable oligomers andpolymers include poly-α-hydroxy acid such as polylactic acid (availablefrom Shimadzu Corporation, commercial name: Lacty, etc) and polyglycolicacid, poly-ω-hydroxyalkanoate such as poly-ε-caprolactone (availablefrom Daicel Chemical Industries, Ltd., commercial name: Placcel, etc.),polyalkylene alkanoate which is a polymer of butylene succinate and/orethylene succinate (available from Showa Highpolymer Co., Ltd.commercial name: Bionole, etc.), polyesters such as polybutylenesuccinate, polyamino acid such as poly-γ-glutamate (Ajinomoto Co., Inc.,commercial name: Polyglutamic acid) and polyols such as polyvinylalcohol and polyethylene glycol. Further, modified bodies of theseartificially synthesized biodegradable oligomers and polymers can bepreferably used.

Examples of naturally synthesized biodegradable oligomers and polymersinclude polysaccharides such as starch, amylose, cellulose, celluloseester, chitin, chitosan, gellan gum, carboxyl group-containingcellulose, carboxyl group-containing starch, pectinic acid and alginicacid; and poly-β-hydroxyalkanoate (available from AstraZeneca,commercial name: Biopol, etc.) which is a polymer of hydroxybutyrateand/or hydroxyvalerate synthesized by a microorganism. Of these, starch,amylose, cellulose, cellulose ester, chitin, chitosan, andpoly-β-hydroxyalkanoate which is a polymer of hydroxybutyrate and/orhydroxyvalerate synthesized by a microorganism are preferred. Inaddition, modified bodies of these naturally synthesized biodegradableoligomers and polymers can be preferably used.

As a derivative of naturally synthesized biodegradable oligomer orpolymer, lignin may be used. Lignin is a dehydrogenated polymer ofconiferyl alcohol or sinapyl alcohol contained in wood in an amount of20 to 30% and is biodegradable.

Of biodegradable resin materials described above, artificiallysynthesized biodegradable oligomers and polymers, derivatives ofartificially synthesized biodegradable oligomers and polymers, andderivatives of naturally synthesized biodegradable oligomers andpolymers are preferably used because they have moderate intermolecularbonding strength, thus exhibit excellent thermoplasticity, do not causeremarkable increase in the viscosity in the melting process and haveexcellent molding processability.

Among these, polyesters and modified polyesters which havethermoplasticity and crystallinity are preferred, aliphatic polyestersand modified aliphatic polyesters are even more preferred, and of thealiphatic polyesters, polylactic acid is excellent in the balance ofproperties and costs. In addition, polyamino acids and modifiedpolyamino acids are preferred, and aliphatic polyamino acids andmodified aliphatic polyamino acids are even more preferred. Further,polyols and modified polyols are preferred, and aliphatic polyols andmodified aliphatic polyols are even more preferred.

An alloy of another thermoplastic resin, e.g., polypropylene,polystyrene, ABS, nylon, polyethylene terephthalate, polybutyleneterephthalate or polycarbonate with the above-mentioned biodegradableresin can be used instead of the biodegradable thermoplastic resin. Inparticular, an alloy of crystalline thermoplastic resin, for example,polypropylene, nylon, polyethylene terephthalate or polybutyleneterephthalate with the above-mentioned biodegradable resin is preferablyused.

In addition, thermosetting resins such as phenol resin, urea resin,melamine resin, alkyd resin, acrylic resin, unsaturated polyester resin,diallylphtharate resin, epoxy resin, silicone resin, cyanate resin,isocyanate resin, furan resin, ketone resin, xylene resin, thermosettingpolyimide, thermosetting polyamide, styrylpyridine resin, nitrileterminated resin, addition curing quinoxaline and addition curingpolyquinoxaline resin, and thermosetting resins using plant materialssuch as lignin, hemicellulose and cellulose can also be reinforced bykenaf fiber. In the case of using thermosetting resin, a curing agent ora curing accelerator necessary for curing may be used.

The kenaf fiber-reinforced resin composition of the present inventioncontains 50 to 90% by mass of the above-described biodegradable resin.Within the range that there is no departure from the spirit and theeffect of the present invention, in addition to the biodegradable resinand the kenaf fiber which are basic constituents, a crystal nucleatingagent and various additives generally added to thermoplastic resin,e.g., an antioxidant, a heat stabilizer, an ultraviolet absorbent, alight stabilizer, an antistatic agent, a neutralizer, a colorant such aspigment, a dispersant, rosin, a plasticizer, a synthetic rubber, aninorganic additive and a flame retardant may be used together. Further,where necessary, an antibacterial agent or an aromatic chemical may beadded to the composition for preventing the kenaf fiber and thebiodegradable resin from being biologically damaged. The antibacterialagent and/or aromatic chemical may be adhered to kenaf fiber in advance.Because the resin composition of the present invention is composedessentially of a kenaf fiber which is a natural material and abiodegradable resin, the crystal nucleating agent and other additivesare also desirably a natural material or a biodegradable materialexcellent in environmental compatibility.

In the present invention, when a crystalline resin is used, it ispreferable to add a crystal nucleating agent to promote crystallizationof amorphous portions which has a low flowing onset temperature, wherebyimprovement in the moldability of the kenaf fiber-reinforced resincomposition, shortening of the molding time and improvement in themechanical strength and the heat resistance of molded articles can beachieved. The crystal nucleating agent itself serves as a crystalnucleus and plays a role to form constituent molecules of the resin intoa regular three-dimensional structure. By adding a crystal nucleatingagent to the resin composition, crystallization of the amorphousportions are promoted, and therefore even when the mold temperature inthe molding process is high, deformation of molded article can besuppressed, and this leads to an effect that the molded article can beeasily released from the mold. In particular, even when the moldtemperature is higher than the glass transition temperature Tg of theresin, a similar effect can be obtained.

As a crystal nucleating agent, an inorganic crystal nucleating agent oran organic crystal nucleating agent may be used. Examples of inorganiccrystal nucleating agent include talc, calcium carbonate, mica, boronnitride, synthetic silicic acid, silicate, silica, kaoline, carbonblack, zinc oxide, montmorillonite, clay mineral, basic magnesiumcarbonate, ground quartz, glass fiber, glass powder, diatomaceous earth,dolomite powder, titanium oxide, zinc oxide, antimony oxide, bariumsulfate, calcium sulfate, alumina, calcium silicate and boron nitride.

Examples of organic crystal nucleating agent include (1) organiccarboxylic acids, for example, octylic acid, toluic acid, heptanoicacid, pelargonic acid, lauric acid, myristic acid, palmitic acid,stearic acid, behenic acid, cerotic acid, montanoic acid, melissic acid,benzoic acid, p-tert-butylbenzoic acid, terephthalic acid, terephthalicacid monomethyl ester, isophthalic acid, isophthalic acid monomethylester, rosin acid, 12-hydroxy stearic acid and cholic acid, (2) organiccarboxylic acid alkali (earth) metal salts, for example, alkali (earth)metal salts of the above-described organic carboxylic acids, (3) highmolecular weight organic compounds containing a metal salt derived froma carboxyl group, for example, metal salts of carboxyl group-containingpolyethylene obtained by oxidation of polyethylene, carboxylgroup-containing polypropylene obtained by oxidation of polypropylene,copolymers of an olefin such as ethylene, propylene or butene-1 andacrylic acid or methacrylic acid, copolymers of styrene and acrylic acidor methacrylic acid, copolymers of olefin and maleic anhydride andcopolymers of styrene and maleic anhydride, (4) aliphatic carboxylicacid amide, for example, oleic acid amide, stearic acid amide, erucicacid amide, behenic acid amide, N-oleylpalmitoamide, N-stearylerucicamide, N, N′-ethylenebis(stearamide), N,N′-methylenebis(stearamide),methylolstearamide, ethylenebisoleic acid amide, ethylene bisbehenicacid amide, ethylene bisstearic acid amide, ethylene bislauric acidamide, hexamethylene bisoleic acid amide, hexamethylene bisstearic acidamide, butylene bisstearic acid amide, N,N′-dioleylsebacic acid amide,N,N′-dioleyladipic acid amide, N,N′-distearyladipic acid amide,N′-distearyl sebacic acid amide, m-xylylene bisstearic acid amide,N,N′-distearyl isophthalic acid amide, N,N′-distearyl terephthalic acidamide, N-oleyl oleic acid amide, N-stearyl oleic acid amide, N-stearylerucic acid amide, N-oleyl stearic acid amide, N-stearyl stearic acidamide, N-butyl-N′ stearyl urea, N-propyl-N′ stearyl urea, N-allyl-N′stearyl urea, N-phenyl-N′ stearyl urea, N-stearyl-N′ stearyl urea,dimethytol oil amide, dimethyl lauric acid amide, dimethyl stearic acidamide, N,N′-cyclohexanebis(stearoamide) and N-lauroyl-L-glutamicacid-α,γ-n-butyl amide, (5) high molecular weight organic compounds, forexample, α-olefins branched at 3-position having 5 or more carbon atomssuch as3,3-dimethylbutene-1,3-methylbutene-1,3-methylpentene-1,3-methylhexene-1,3,5,5-trimethylhexene-1,polymers of vinylcycloalkane such as vinylcyclopentene, vinylcyclohexaneand vinylnorbornane, polyalkylene glycols such as polyethylene glycoland polypropylene glycol, polyglycolic acid, cellulose, cellulose ester,cellulose ether, polyester and polycarbonate, (6) organic phosphate orphosphite compounds or a metal salt thereof, for example, diphenylphosphate, diphenyl phosphite, sodium bis-(4-tert-butylphenyl) phosphateand sodium methylene(2,4-tert-butylphenyl) phosphate, (7) sorbitolderivatives such as bis(p-methylbenzylidene)sorbitol andbis(p-ethylbenzylidene) sorbitol, (8) cholesterol derivatives such ascholesteryl stearate and cholesteryloxystearamide, and (9) thioglycolicanhydride, paratoluene sulfonic acid, paratoluene sulfonic acid amideand a metal salt thereof.

Biodegradable resins such as polylactic acid that can be used in thepresent invention is what is termed polyester resin, of which themolecular weight is decreased upon hydrolysis. Accordingly, of theabove-mentioned crystal nucleating agents, crystal nucleating agentscomposed of a neutral substance which do not facilitate the hydrolysisof polyester are preferably used. In addition, to prevent decrease inmolecular weight of polyester resin due to transesterification, ratherthan a carboxyl group-containing crystal nucleating agent, an ester oramide compound which is a derivative thereof is preferred as a crystalnucleating agent, and similarly, rather than a hydroxyl group-containingcrystal nucleating agent, an ester or ether compound which is aderivative thereof is preferred as a crystal nucleating agent.

An organic crystal nucleating agent which is compatible with or finelydispersed in resin at a high temperature melting condition in injectionmolding, and precipitated or phase-separated in a mold in the moldcooling step to serve as a crystal nucleating agent is preferably used.As a method of adding a crystal nucleating agent, a common method is tomix the agent with resin directly, but the agent may be previouslyadhered to granular or fibrous additive, or kenaf fiber. In particular,when an organic crystal nucleating agent is uniformly adhered to thefiber, crystallization of resin on the surface of the fiber is promotedand the intensity of detaching fiber is increased, and as a result,strength properties such as impact strength of a resin containing thesefibers may be improved. Further, an inorganic crystal nucleating agentefficiently acts as a crystal nucleus when fine particles of suchinorganic substance are highly dispersed in the resin. The surface ofsuch inorganic substance is preferably subjected to a solubilizingtreatment (coating treatment using resin or a compound having asolubilizing effect, or ion exchange treatment or surface treatment by acoupling agent). Inorganic crystal nucleating agents which haveundergone a solubilizing treatment has increased dispersibility due tothe increased interaction with resin and is capable of preventingagglomeration of the inorganic compound.

Of these crystal nucleating agents, layered compounds such as talc arepreferred. Further, an inorganic crystal nucleating agent and an organiccrystal nucleating agent may be used together. Plural kinds of thesecrystal nucleating agents may be used together.

The content of the crystal nucleating agent of the kenaffiber-reinforced resin composition of the present invention ispreferably 0.1 to 20% by mass, but not particularly limited.

The method of mixing the components contained in the kenaffiber-reinforced resin composition of the present invention is notparticularly limited, and examples thereof include mixing using a knownmixer such as a tumbler or a ribbon blender, and melt-mixing using anextruder or a roll.

The method of molding the kenaf fiber-reinforced resin composition ofthe present invention is not particularly limited, and usual moldingmethods for producing electrical and electronic equipment products, suchas known injection molding, injection/compression molding andcompression molding may be used.

The temperature of melt-mixing and molding can be selected from atemperature at which the resin to be used is softened to 200° C. Whenthe temperature is higher than 200° C., the kenaf fiber suffers fromthermal degradation, which may decrease the reinforcing effect.

However, when using kenaf fiber with improved heat resistance bysubjecting to surface treatment, thermal degradation of the kenaf fibercan be suppressed and melt-kneading and molding can be thus carried outat 200° C. or higher. Further, in the case that a lubricant which has amelting point lower than the mold processing temperature is usedtogether, melt-kneading and molding can be also carried out at 200° C.or higher. The reason is that since low melting point lubricant iseasily dispersed in the resin and easily adhered to the surface of kenaffiber, it can impart lubricity to the resin and the kenaf fiber, and asa result, shear heating generated between kenaf fibers or between thekenaf fiber and the resin, and friction with the mold surface can bereduced. The reduction of shear heating and frictional heat bycombination use of a low melting point lubricant suppresses localtemperature rise in the resin, which then prevents fiber from beingdeteriorated and makes it possible to mold at 200° C. or higher.

EXAMPLES

The operation of the present embodiment will now be described referringto specific Examples.

Example 1

As a kenaf fiber, a bast fiber (kenaf fiber prepared only from bast) wasused. The kenaf fiber had an average fiber length of 3 to 5 mm (numberaverage fiber length of the fibers excluding fragments (those less than50 μm in the length in the longitudinal direction)). FIG. 1 is amicrograph of the bast fiber (kenaf fiber prepared only from bast) usedin this Example, and FIG. 2 is a micrograph of the same bast fiber atdifferent magnification.

10% by mass of this bast fiber and 90% by mass of polylactic acid(available from Shimadzu Corporation, Lacty 9030) were each dried at100° C. for 5 hours and melt-kneaded in a kneader (S1 Kneader made byKURIMOTO, LTD. kneading temperature: 180° C.) to give pellets. Theobtained pellets were dried at 100° C. for 5 hours and molded in aninjection molding machine (made by TOSHIBA MACHINE CO., LTD, EC20P-0.4A,molding temperature: 180° C., metal mold temperature: 25° C.), to formtest pieces (125×13×3.2 mm).

The test pieces were left in a thermostatic chamber at 100° C. for 4hours and cooled to room temperature to measure the heat distortiontemperature and the flexural modulus. The heat distortion temperaturewas measured at a high load (1.80 MPa) in accordance with JIS K 7191-2.The flexural modulus was measured in accordance with ASTM D790. Theresults are shown in Table 1.

Examples 2 to 4

The ratio of the bast fiber to the polylactic acid in Example 1 waschanged to bast fiber/polylactic acid=15/85, 20/80, 30/70 (all in massratio), and the other conditions were the same as in Example 1. Thereinforcing effect of bast fiber on polylactic acid was evaluated in thesame manner as in Example 1, and the results are shown in Table 1.

As shown in Table 1, it has been revealed that by incorporating the bastfiber, the flexural modulus of polylactic acid can be improved in thesame level of kneadability as that of polylactic acid, and inparticular, the heat distortion temperature at high loads can be greatlyimproved. In addition, as shown in Table 1, in the case of polylacticacid containing bast fiber, the flexural modulus of the polylactic acidcould be improved with the same level of kneadability as that ofpolylactic acid. In particular, it has been found that when the contentof the bast fiber was 15% by mass or more, the heat distortiontemperature (heat resistance) at high loads can be greatly improved.When the content of the bast fiber is 20% by mass or higher, theimprovement in the heat distortion temperature was peaked, but theflexural modulus was further improved. The measured values wereassociated with no variation and thus exertion of stable reinforcingeffect was confirmed.

Example 5

A whole stem fiber prepared from bast and xylem was used instead of thebast fiber in Example 1. The conditions were otherwise the same as inExample 1 and the results are shown in Table 1.

FIG. 3 is a micrograph of the whole stem fiber used. The whole stemfiber had an average fiber length of 100 to 200 μm, but the fiber alsocontained long fibers of 1 mm or more. The long fibers came from bast.The sample using whole stem fiber also had a reinforcing effectindicated by the flexural modulus equivalent to that of bast fiber asshown in Table 1. On the other hand, the improvement in the heatresistance indicated by the heat distortion temperature was not asexcellent as that of the bast fiber. Although studies are not complete,it is assumed that the bast fiber which is a long fiber of mm-leveleffectively contributed to the improvement in the heat resistance.

Comparative Example 1

A flax fiber which is a soft fiber as kenaf fiber was used instead ofthe bast fiber in Example 1. The conditions were otherwise the same asin Example 1 and the results are shown in Table 1. As shown in Table 1,it has been revealed that those containing 15% by mass of flax fiber hada reinforcing effect only about the same as that of those containing 10%by mass of bast fiber. The reason is assumed to be that the strength ofthe flax fiber is lower than that of the kenaf fiber.

Comparative Examples 2 to 3

In Comparative Example 2, the ratio of the kenaf fiber to the polylacticacid in Example 1 was changed to kenaf fiber/polylactic acid=5/95 (massratio). The conditions were otherwise the same as in Example 1 and theresults are shown in Table 1. As shown in Table 1, it has been foundthat when the content of the bast fiber is 5% by mass or less, thereinforcing effect is hardly obtained and when the content of the bastfiber is in between 5% by mass and 10% by mass, the flexural modulus issignificantly improved.

In Comparative Example 3, the ratio of the kenaf fiber to the polylacticacid in Example 1 was changed to kenaf fiber/polylactic acid=60/40 (massratio). The conditions were otherwise the same as in Example 1. Althoughevaluation was attempted in the same manner as in Example 1, pelletizingin the kneading process was difficult and the evaluation following themolding was impossible.

TABLE 1 Ref. Com. Com. Com. Ex. Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 1 Ex.2 Ex. 3 Bast fiber (% by mass) — 10 15 20 30 — — 5 60 Whole stem fiber(% by mass) — — — — — 15 — — — Flax fiber (% by mass) — — — — — — — —Polylactic acid (% by mass) 100 90 85 80 70 85 85 95 40 Kneadability (*)∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ x Heat distortion temperature 66 72 108 121 122 98 74 69Cannot (° C.) (load: 1.8 MPa) be measured Flexural modulus (GPa) 4.545.40 6.25 7.60 8.64 6.28 5.69 4.56 Cannot be measured *∘: Kneadabilityis good (pelletizable in the melt-kneading process) x: Kneadability ispoor (not pelletizable in the melt-kneading process)

Example 6

The ratio of the kenaf fiber to the polylactic acid in Example 1 waschanged to kenaf fiber/polylactic acid=15/85 (mass ratio), and pelletsusing 5% by mass of talc together based on 95% by mass of the kenaffiber and the polylactic acid were prepared in the same manner as inExample 1. The obtained pellets were dried at 100° C. for 5 hours andmolded into a test piece (125×13×3.2 mm) using an injection moldingmachine (made by TOSHIBA MACHINE CO., LTD, EC20P-0.4A, moldingtemperature: 180° C., metal mold temperature: 100° C.). As a result, ithas been revealed that by using a crystal nucleating agent together,moldability at high mold temperatures can be improved.

Examples 7, 8, 9

A bast fiber (average fiber length 3 to 5 mm, hereinafter bast fiber 2)from which fragments were removed, a bast fiber having an average fiberlength of 5 mm (hereinafter bast fiber 3), a flexibilizer (availablefrom Dainippon Ink and Chemicals, Incorporated, PD-150) and polylacticacid (available from Shimadzu Corporation, Lacty 9030) were each driedat 100° C. for 5 hours, and melt-kneaded according to the compositionshown in Table 2 using a kneader (S1 Kneader made by KURIMOTO, LTD.kneading temperature: 180° C. ) to give pellets. The obtained pelletswere dried at 100° C. for 5 hours and molded into test pieces(125×13×3.2 mm) using an injection molding machine (made by TOSHIBAMACHINE CO., LTD, EC20P-0.4A, molding temperature: 180° C., metal moldtemperature: 25°C. ). The obtained test pieces were left in a thermostatchamber at 100° C. for 4 hours and cooled to room temperature and thenotched Izod impact strength was measured.

As shown in Example 7 of Table 2, the impact strength was improved bythe use of the flexibilizer. As shown in Examples 8 and 9, removal offragments also led to improvement in the impact strength.

TABLE 2 Ref. Ref. Ref. Ex. 1 Ex. 2 Ex. 3 Ex. 7 Ex. 8 Ex. 9 Bast fiber 1— 20 — 20 — — (containing fragments, % by mass) Whole stem fiber — — 20— — — (% by mass) Bast fiber 2 — — — — 20 — (containing no fragments, %by mass) Bast fiber 3 (cut into 5 mm, — — — — — 20 % by mass)Flexibilizer — — — 20 — — (% by mass) Polylactic acid (% by mass) 100 8080 60 80 80 Impact strength (kJ/m²) 4.4 3.1 1.6 3.9 3.8 4.2

Example 10

Using a bast fiber dried at 100° C. for 5 hours (product similar to thebast fiber of Example 1), toluene diisocyanate (1/10 the amount of kenafin weight ratio) was added thereto and mixed in chloroform (about 10times the amount of kenaf in weight ratio) for a pre-determined time (8hours). Chloroform was then removed to give surface-treated kenaf fiber.

20% by mass of the surface-treated kenaf fiber and 80% by mass ofpolylactic acid (available from Shimadzu Corporation, Lacty 9030) wereeach dried at 100° C. for 5 hours, and melt-kneaded using a kneader (S1Kneader made by KURIMOTO, LTD. kneading temperature: 180° C.) to givepellets. The obtained pellets were dried at 100° C. for 5 hours andmolded into a test piece (125×13×3.2 mm) using an injection moldingmachine (made by TOSHIBA MACHINE CO., LTD, EC20P-0.4A, moldingtemperature: 180° C., metal mold temperature: 25° C.).

The obtained test piece was left in a thermostat chamber at 100° C. for4 hours and cooled to room temperature and the notched Izod impactstrength was measured. The measurement of the notched Izod impactstrength was carried out in accordance with JISK7110. As a result, theimpact strength was 3.6 kJ/m² (impact strength of non-treated fiber: 3.1kJ/m²).

The present invention is not limited to the above-described Examples andit is obvious that these Examples can be accordingly modified within thetechnical scope of the present invention.

INDUSTRIAL APPLICABILITY

As described above, according to the kenaf fiber-reinforced resincomposition of the present invention, by incorporating a specific amountof a kenaf fiber having a fiber length of not more than 20 mm into abiodegradable resin, preferably a biodegradable thermoplastic resin, amolding process necessary for manufacturing electrical and electronicequipment products can be suitably applied. In addition, while themechanical strength of the molded article molded using the kenaffiber-reinforced resin composition of the present invention can beimproved, the heat resistance can be also significantly improved.Further, since the resin composition of the present invention contains akenaf fiber, the shrinking percentage of a biodegradable resin,particularly biodegradable thermoplastic resin can also be reduced.

1. A kenaf fiber-reinforced resin composition, characterized in that thecomposition is a biodegradable resin composition containing a kenaffiber and contains the kenaf fiber in an amount of 10 to 50% by massbased on the mass of the fiber-reinforced resin composition, wherein amoisture content of the kenaf fiber is not more than 4% by mass based onthe mass of the kenaf fiber.
 2. The kenaf fiber-reinforced resincomposition according to claim 1, characterized in that the content ofthe kenaf fiber is 15 to 40% by mass based on the mass of thefiber-reinforced resin composition.
 3. The kenaf fiber-reinforced resincomposition according to claim 1, characterized in that thebiodegradable resin is a crystalline thermoplastic resin.
 4. The kenaffiber-reinforced resin composition according to claim 1, characterizedin that the biodegradable resin is polylactic acid.
 5. The kenaffiber-reinforced resin composition according to claim 1, characterizedin that the kenaf fiber has an average fiber length (number averagefiber length of the fibers excluding fragments) of 100 μm to 20 mm. 6.The kenaf fiber-reinforced resin composition according to claim 5,characterized in that the kenaf fiber contains a kenaf fiber having afiber length of 300 μm to 20 mm.
 7. The kenaf fiber-reinforced resincomposition according to claim 1, characterized in that the kenaf fiberis prepared from bast of kenaf.
 8. The kenaf fiber-reinforced resincomposition according to claim 2, characterized in that thebiodegradable resin is a crystalline thermoplastic resin.
 9. The kenaffiber-reinforced resin composition according to claim 2, characterizedin that the biodegradable resin is polylactic acid.
 10. The kenaffiber-reinforced resin composition according to claim 3, characterizedin that the biodegradable resin is polylactic acid.
 11. The kenaffiber-reinforced resin composition according to claim 2, characterizedin that the kenaf fiber has an average fiber length (number averagefiber length of the fibers excluding fragments) of 100 μm to 20 mm. 12.The kenaf fiber-reinforced resin composition according to claim 3,characterized in that the kenaf fiber has an average fiber length(number average fiber length of the fibers excluding fragments) of 100μm to 20 mm.
 13. The kenaf fiber-reinforced resin composition accordingto claim 4, characterized in that the kenaf fiber has an average fiberlength (number average fiber length of the fibers excluding fragments)of 100 μm to 20 mm.
 14. The kenaf fiber-reinforced resin compositionaccording to claim 2, characterized in that the kenaf fiber is preparedfrom bast of kenaf.
 15. The kenaf fiber-reinforced resin compositionaccording to claim 3, characterized in that the kenaf fiber is preparedfrom bast of kenaf.
 16. The kenaf fiber-reinforced resin compositionaccording to claim 4, characterized in that the kenaf fiber is preparedfrom bast of kenaf.
 17. The kenaf fiber-reinforced resin compositionaccording to claim 5, characterized in that the kenaf fiber is preparedfrom bast of kenaf.
 18. The kenaf fiber-reinforced resin compositionaccording to claim 6, characterized in that the kenaf fiber is preparedfrom bast of kenaf.